Core of an IPTV

The backbone or core of an IPTV networking infrastructure is required to carry large volumes of video content at high speed between the IPTV data center and the last mile broadband distribution network. There are several different types of backbone transmission standards that provide multipath and link protection capabilities that are necessary to ensure high reliability capabilities. Each standard has a number of specific features including data transfer speed and scalability.
Three of the major backbone transmission technologies used in IPTV network infrastructures are ATM over SONET/SDH, IP over MPLS and metro Ethernet. As FIGURE 2.13 IPTV core-networking infrastructure.

IPTV BACKBONE TECHNOLOGIES
illustrated in Fig. 2.13 these core networking technologies provide connectivity between the centralized IPTV data center and various types of access networks.

ATM and SONET/SDH
As described, ATM can support demanding applications such as IPTV that require high bandwidth and low transmission delays. ATM will operate over different network media including coaxial and twisted pair cables, however, it runs at its optimum speed over fiber optic cable. A physical layer called Synchronous Optical Network (SONET) is typically used by a number of telecommunication carriers to transport ATM cells over the backbone network.

SONET is a protocol that provides high speed transmission using fiber optic media. The term Synchronous Digital Hierarchy (SDH) refers to the optical technology outside the United States. The SONET signal rate is measured by optical carrier (OC) standards. Table 2.7 illustrates the available transmission rates(called OC levels).

SONET uses time division multiplexing (TDM) to send multiple data streams simultaneously. With TDM, the SONET network allocates bandwidth to a certain portion of time on a specific frequency. The preassigned time slots are active regardless of whether there is data to transmit.
In the context of an IPTV networking environment the SONET equipment receives a number of bit streams and combines into a single stream, which then is sent out onto the fiber network using a light emitting device. The rates of the combined input rates will equal the rate outputted from the SONET device. For example, four input streams carrying IPTV traffic at 1 Gbps will be combined by the SONET device and a 4 Gbps stream is forwarded onto the fiber network.

IP and MPLS
A number of larger telecommunication companies have started to deploy the Internet Protocol in their core networks. Although IP was never originally designed TABLE 2.7 SONET Optical Carrier Standards
OC level Signal Transmission Rate
OC-1 (base rate)51.84 Mbps
OC-3 155.52 Mbps
OC-12 622.08 Mbps
OC-24 1.244 Gbps
OC-48 2.488 Gbps
OC-192 10 Gbps
OC-256 13.271 Gbps
OC-768 40 Gbps

with features such as QoS and traffic segregation capabilities the protocol works quite well in these environments when combined with a technology called Multiprotocol Label Switching (MPLS). An MPLS enabled network supports the efficient delivery of various video traffic types over a common networking platform.
An MPLS platform is designed and built using advanced Label Switch Routers (LSRs). These LSRs are responsible for establishing connection-oriented paths to specific destinations on the IPTV network. These virtual paths are called Label Switched Paths (LSPs) and are configured with enough resources to ensure the smooth transition of IPTV traffic through an MPLS network. The use of LSPs simplifies and speeds up the routing of packets through the network becau se deep packet inspection only occurs at the ingress to the network and is not required at each router hop.
The other main function of LSRs is to identify network traffic types. This is achieved by adding a MPLS header onto the beginning of each IPTV packet.
As illustrated in Fig. 2.14 the header is added at the ingress LSR and removed by the egress LSR as it leaves the MPLS core network. While the IPTV traffic traverses across MPLS enabled routers a number of local tables called Label Information Bases (LIBs) are consulted to determine details about the next hop along the route. In addition to examining the table, a new label is applied to the packet and forwarded onward to the appropriate router o utput port.
Other added benefits of MPLS networks include their support for high levels of resilience when a failure occurs.

Metro Ethernet
Another technology, which may be deployed in the core network, is Metro Ethernet. An alliance of leading service providers, equipment vendors, and other TABLE 2.8 MPLS Header Format Field Name Field Length (Bits) Description of Functionality Label 20 Contains specific next hop routing details that are specific to each IPTV packet.
Experimental bits 3 Reserved for other uses.
Stacking bit 1 A header can contain one or more labels. Once the stacking bit is set to one, the LSR will identify the last label in the packet.
Time to live (TTL) 8 This value is copied from the TTL field in the IP header.

MPLS core network topology
prominent networking companies called the Metro Ethernet Forum (MEF) isresponsible for establishing specifications for integrating Ethernet technologies intohigh capacity backbone and core networks. In addition to developing specificationsthe MEF also certifies Ethernet equipment for use in service provider’s corenetworking infrastructures. The key technical and operational characteristics of
Metro Ethernet based core networks include:
. It meets the various requirements that are typical of a core networkingtechnology, namely, resilience, high performance, and scalability.
. Some of the modern Metro Ethernet networking components can operate atspeeds up to 100 Gbps across long geographical distances. This providesservice providers with an ideal platform for efficiently delivering newvalue-added services such as IPTV to geographically dispersed regionaloffices.
. It implements a sophisticated recovery mechanism in the event of a networklink failure thereby, ensuring that services such as IPTV are unaffected by theoutage.
. Metro Ethernet technologies support the use of connection orientated virtualcircuits that allow IPTV service providers to guarantee the delivery of highquality video content within the network core. These dedicated links are calledEthernet Virtual Connections (EVCs). Figure 2.15 shows how four EVCs areused to provide connectivity between the IPTV data center and a number ofregional offices.
In addition to the above characteristics, the low delay and packet loss features ofMetro Ethernet make it an ideal core networking technology for carrying IPTVservices.